The present disclosure is directed generally to micro-electro-mechanical systems (MEMS) devices and, more particularly, to processing techniques for forming ultrathin devices.
The ability to form moving parts measured in microns has opened up a huge range of applications. Such moving parts typically take the form of a beam or mesh that may form, for example, a variable capacitor, switch, or other component. The recent ability to seal micro-machined meshes has lead to the fabrication of microphones and microspeakers. See, for example, International Publication No. WO/01/20948 A2 published 22 Mar. 2001, entitled MEMS Digital-to-Acoustic Transducer With Error Cancellation, the entirety of which is hereby incorporated by reference.
A sealed mesh can function as a movable plate of a variable capacitor, and therefore can operate as a microspeaker or microphone. For a sealed mesh to operate as a microspeaker or microphone, the device needs to be able to push air to create a soundwave just as its larger counterparts must push air to create soundwaves. For example, traditional speaker enclosures have a port on the back to allow the speaker to move freely. In the case of a microspeaker or microphone, if the chamber beneath the sealed mesh does not have a vent or other opening to ambient, movement of the sealed mesh inward is inhibited by the inability to compress the air in the chamber while movement of the mesh outward is inhibited by formation of a vacuum. Thus it is necessary to form a vent in the chamber.
Currently, such vents are formed by boring through the substrate from the rear. That requires patterning the back side of the substrate followed by an etch through the entirety of the substrate to reach the chamber. Forming of vents by this technique is slow in that several hundred microns of substrate may need to be etched to reach the chamber beneath the sealed mesh and the diameter of the vent is small compared to its depth. Additionally, there are registration problems in that it is necessary to work from the back side of the substrate where there are no landmarks, and hundreds of microns may need to be etched to reach a chamber that may measure in the tens of microns.
U.S. patent application Ser. No. 10/349,618 entitled Process for Forming and Acoustically Connecting Structures on a Substrate, filed Jan. 23, 2003 discloses a processes in which the substrate is etched in the area of the mesh. Although that represents an improvement over the prior art, the need still exists for an easy, repeatable, fast process for forming vents in the chambers of sealed meshes that are to function as speakers or microphones.